Use of Fungal Laccases and Peroxidases for Enzymatic Treatment of Wastewater Containing Synthetic Dyes - Green Chemistry for Dyes Removal from Wastewater - page 204

synthetic dyes are organic compounds with multiple aromatic rings, either
fused or connected by covalent bonds, and modified by various hydrophilic
functional groups, such as amine, carbonyl, carboxylic acid, and hydroxyl
groups, to produce desired colors, increase the affinity to the materials
being dyed, and improve the solubility in solvents, such as water, during
dyeing processes. Being synthetic organics, those dyes are often resistant to
biodegradation in engineered treatment processes such as activated sludge,
as well as in the natural aquatic environment [1-3]. As a result, the pollu-
tion of the aquatic environment by residual synthetic dyes discharged to
water bodies via industrial effluents has been a major environmental and
public health issue in many countries such as India, Pakistan, Indonesia,
and China, where the textile industry has been growing steadily [4-7].
Such dye pollution in the rivers and lakes tends to intensify especially in
small townships and villages where many smaller factories are present, and
pollution prevention measures, such as wastewater treatment, have not
been implemented because effective regulations are absent [8,9].
Colored water due to untreated and partially treated industrial efflu-
ents containing synthetic dyes is not only aesthetically unappealing and
unpleasant, but can also cause many undesired adverse impacts on the
receiving environment and public health. While many synthetic dyes are
relatively nontoxic, some of their degradation byproducts, such as ani-
lines, are often more toxic and sometimes carcinogenic than the parent
compounds [5,10,11]. In addition to the toxicity, residual organic dyes can
also exert various hazards on the aquatic ecosystem by depleting dissolved
oxygen, blocking sunlight penetration, and inhibiting photosynthesis and
growth of aquatic organisms. Therefore, effective treatment methods for
textile wastewater containing synthetic dyes have been sought over the past
several decades [2].
A number of physical, chemical, and biological treatment processes
have been investigated for the removal and/or destruction of synthetic
dyes. For example, chemical oxidation, such as ozonation and Fenton pro-
cesses, electrocoagulation/electro-oxidation, adsorptive treatment using
granular activated carbon and other plant-derived materials, aerobic and
anaerobic processes, such as activated sludge, and membrane filtration,
such as reverse osmosis and nanofiltration, have been found to be effec-
tive [1,12,13]. The enzymatic process using ligninolytic enzymes, such as
laccases and peroxidases, is a relatively new emerging technology for the
degradation of xenobiotics, including synthetic dyes in textile wastewa-
ter [14-16]. This unique process employs a hybrid of chemical and bio-
logical oxidation using a combination of crude or purified enzymes from
plant materials or fungal cultures as a biocatalyst and dissolved molecular